Standard threaded torque fastener with novel indentation patterns to enhance torque and self-locking capabilities

ABSTRACT

The novel concept to be patented involves minutely indenting the standard fasteners along the pitch line at various points and utilizing the small material deformations around these indentations to provide substantial engagement to resist loosening of the joint under operational loads. The basic idea is to stamp a typical pattern (two are described below) on the fastener to achieve the advantages of a self-locking mechanism as well as enhance the torque and load carrying capability of the joint. Moreover, the indentations being in the order of few mils would not degrade the strength of the fastener, but would continue to provide sufficient load transfer across the joint without loss of preload. Furthermore, the joint can be disassembled and the fasteners can then be reused for the subsequent operations. These unique indentations on the fasteners can be of varying numbers, depths, geometry (spherical, elliptical etc.) and of various patterns (linear, staggered etc.) as dictated by the requirements of an application. The fastener can then withstand a considerable high temperature stress depending on its material composition/alloy. Lastly, the fastener can also withstand moderate to intense vibration depending on the added torque value by decreasing or increasing the number of indentations. In summary, the uniqueness of our concept lies in utilizing these indentation patterns in a simpler inexpensive way to achieve self-locking capability and meet the life cycle requirements of the joint for any given engineering application.

CROSS REFERENCE TO RELATED APPLICATION

[0001] While searching for related work, we looked at 1) structure, 2)function and 3) the overall appearance of other inventions compared tothe novelty of our present invention. Structural considerations involvedhow it really works and how it is put together and what different partsare used in the construction. Functional considerations involved lookingat what one specific invention does and to what extension itaccomplishes the objective. Finally, overall appearances involvedwhether prior patents looked substantially different. The conclusion isthat there has been no such invention to our knowledge that directlyresembles our concept in structure and extent of the function ordesign/appearance. The ones that are relevant to a little extent in thisarea are described below.

[0002] Prior work done by Nason et al. [1], Criswell [2] and Orlomoski[3] is related to the present invention and is only relevant to theextent that a similar function is disclosed. Their invention providesthe function of self-locking but there are inherent structuraldifferences in their design and invention with ours, and is verydifferent from the one, proposed here in function and appearance.

[0003] Another company called Long-Lok [4] uses nylon type patching ofvarious shapes on a wide range of their metal fasteners to achieveself-locking. This is in contrast to ours where we make use of theunique indentation patterns. Another type of Long-Lok fasteners calledDyna-Thread II, makes obvious reference to their patented design (withno patent number provided in the reference handbook) and has been usingbolts with the periphery of its controlled thread area dilated toproduce the desired torque. Additionally, the configuration of thisfastener with an axial hole for dilation renders it absolutelyunsuitable for high strength application. Furthermore, such dilatedbolts experience lower strength capabilities (due to a very thin wall)on the dilated surface and under mechanical loading, could lead to ashear failure due to a reduced load transfer or fail in fatigue undervibratory loads. Finally, these Dyna-Thread II fasteners are veryexpensive as well.

[0004] The remaining patents to Matsunami [5], Iwata [6] are provided asa general interest and are also pertinent to the construction and designof the invention. They do not render obvious self-locking fasteners ofthe present invention.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0005] Federally sponsored R&D work has not been done on the abovesubject to this date.

REFERENCE TO SEQUENCE LISTING, A TABLE OR A COMPUTER PROGRAM

[0006] None.

BACKGROUND OF THE INVENTION

[0007] Working in the American automotive and aerospace industries fordecades, the authors identified a problem with the fastener-joints to besolved, and this prompted them into this innovation process.

[0008] The fasteners most commonly used in various industries(automotive, aerospace etc.) do not provide adequate torque andself-locking features to resist loss of preload or axial tension underdynamic/vibratory loading.

[0009] Few predecessors tried to incorporate various features to addself-locking capabilities to the joints. In particular, Nylok andLonglok fasteners that are already in use provide torque that issuitable up to moderate temperature (250° F.) applications. Anothergroup of fasteners called Dyna-thread II was designed such that theperiphery of its controlled thread area is dilated to produce thedesired torque. Even though it can be used as a high temperatureapplication, there is a limitation on the size of the bolt itself (1″O.D./nominal size max.). Additionally, on such fasteners, it becomesdifficult to control the expansion of threaded area as the nominaldiameter of the bolt increases. Furthermore, as such engineeringapplications may need higher torque, one may need to increase thedilation of the thread but that in turn gets cumbersome as the boltdiameter increase (1″ O.D./nominal size max.).

[0010] In addition to the above concerns, dilated fasteners experiencelower strength capabilities (due to a very thin wall) on the dilatedsurface compared to the rated strength capabilities at the full crosssection of the fastener. Lastly, under mechanical loading, suchdilations could lead to a shear failure due to a reduced load transferor result in a fatigue failure of the fastener due to repeated loadingand unloading.

BRIEF SUMMARY OF THE INVENTION

[0011] The concept presented above enhances the torque carrying andself-locking capabilities of mechanical joints without appreciablydegrading the fatigue life of the indented bolt and maintaining safetyfactor of the mechanical joint in operation.

[0012] In our proposed concept, the threaded fastener is indented alongits pitch line at various points and the material deformation aroundthese indentations are utilized to provide substantial engagement whichhelps the joints in withstanding moderate to intense vibrations. Theconcept incorporates the following ideas:

[0013] a) Varying the number of indentations

[0014] b) Controlling the depth of indentations

[0015] c) Geometry of the indentations depending on the tool designedfor this purpose and

[0016] d) Varying the pattern of indentations to suit the application

[0017] These indentations unlike the concepts discussed previously, areminute and hence would cause a minimal loss of strength and can bemapped to vary the range of torque required for the intendedapplications.

[0018] Such self-locking fasteners when properly designed, engineeredand installed will virtually eliminate loss of preload and jointseparation under dynamic/vibratory loads which otherwise have caused aloosening of the mechanical joints.

BRIEF DESCRIPTION OF THE DRAWING

[0019]FIG. 1 delineates a virgin fastener without thread indentations.

[0020] In FIG. 2, spherical indentations have been marked on fiveconsecutive threads.

[0021] In FIG. 3, spherical indentations have been marked in a staggeredmanner. Each of these figures represents a family of indentationpatterns. End F represents the left-hand side of each of thesefasteners.

[0022]FIG. 1 shows the threaded portion of a common fastener. In FIG. 2,spherical indentations have been marked in five consecutive threads toconstitute a linear pattern. In FIG. 3, spherical indentations have beenmarked in a staggered manner. Each of these FIGS. 2 and 3 represents afamily of indentation patterns and are described below.

[0023] Linear Pattern:

[0024] In FIG. 2, six indentation marks have been made peripherallyalong the pitch circle diameter of the fastener for a single pitch ofthe thread. First pair of indentations (A₁, A₁′) starts at a distance of1½ thread from the face F of the fastener. Similarly, other fiveindentations [(A₂, A₂′), (A₃, A₃′), (A₄, A₄′), (A₅, A₅′), (A₆, A₆′)] arealso performed peripherally at an included angle of 60° for consecutivepair of indentations. Thus six pair of indentation marks are stampedbeginning from (A₁, A₁′).

[0025] The next set of indentation (B₁, B₁′) begins from the adjacentthread at an angle of 60° from (A₁, A₁′) with respect to the axes of thefastener. Then, other 5 indentations [(B₂, B₂′), (B₃, B₃′), (B₄, B₄′),(B₅, B₅′), (B₆, B₆′)] are performed peripherally at an included angle of60° for consecutive pair of indentations. Thus six pair of equidistantindentation marks are formed beginning consecutively from (B₁, B₁′.Similarly, six pair of equidistant indentation marks are formedbeginning consecutively from (C₁, C₁′), (D₁, D₁′), (E₁, E₁′) at an angleof 60° with respect to the axes of the fastener. Hence, there is anarray of indentations beginning from (A₁, A₁′), (B₁, B₁′), (C₁, C₁′),(D₁, D₁′), (E₁, E₁′) which forms a linear indentation pattern.

[0026] Please note that in FIG. 2, among the six pair of indentations ona first full/360′ thread, only two: (A₁, A₁′) and (A₆, A₆′) are shown.The other intermediate indentations at 60° intervals, namely (A₂, A₂′)through (A₅, A₅′) are not shown for simplicity in illustration.Similarly, (B₂, B₂′) through (B₆, B₆′), (C₂, C₂′) through (C₆, C₆′),(D₂, D₂′) through (D₆, D₆′) and (E₂, E₂′) through (E₆, E₆′) are notshown as well to keep clarity in the diagram.

[0027] Staggered Pattern:

[0028] In FIG. 3, six indentation marks have been made peripherallyalong the pitch circle diameter of the fastener for a single pitch ofthe thread. First pair of indentations (A₁, A₁′) starts at a distance of1½ thread from the face F of the fastener. Similarly, other fiveindentations [(A₂, A₂′), (A₃, A₃′), (A₄, A₄′), (A₅, A₅′), (A₆, A₆′)] arealso performed peripherally at an included angle of 60° for consecutivepair of indentations. Thus six pair of indentation marks are stampedbeginning from (A₁, A₁′).

[0029] The next set of indentation (C₁, C₁′) begins by skipping theadjacent thread and making an angle of 15° from (A₁, A₁′), with respectto the axis of the fastener. The other five indentations [(C₂, C₂′),(C₃, C₃′), (C₄, C₄′), (C₅, C₅′), (C₆, C₆′)] are performed peripherallyat an included angle of 60° for consecutive pair of indentations. Thussix pair of indentations marks are formed beginning from (C₁, C₁′) andculminating at (C₆, C₆′). Similarly, skipping the following thread, sixpair of indentation marks are formed making an angle of 15° from (C₁,C₁′) with respect to the axes of the fastener beginning from (E₁, E₁′)and culminating at (E₆, E₆′). Now, a staggered set of indentations areformed beginning from (B₁, B₁′) such that the marks (B₁, B₁′) and (C₁,C₁′) are equidistant from this starter (A₁, A₁′). Thus six pair ofequidistant marks are formed beginning from (B₁, B₁′) and culminating at(B₆, B₆′). Finally, skipping the adjacent thread and making an angle of15° from (B₁, B₁′) with respect to the axes of the fastener, six pair ofindentation marks are formed beginning from (D₁, D₁′) and ending at (D₆,D₆′). Hence, there are two arrays of indentations beginning from (A₁,A₁′), (C₁, C₁′), (E₁, E₁′) which forms a linear indentation pattern andthe other begins from (B₁, B₁′), (D₁, D₁′) which forms a linearindentation pattern as well in a staggered fashion.

[0030] Please note that in FIG. 3, among the six pairs of indentationson the first 360° thread, only two: (A₁, A₁′) and (A₆, A₆′) are shown.The other intermediate indentations at 60° intervals, namely (A₂, A₂′)through (A₅, A₅′) are not shown for simplicity in illustration.Similarly, (B₂, B₂′) through (B₆, B₆′), (C₂, C₂′) through (C₆, C₆′),(D₂, D₂′) through (D₆, D₆′) and (E₂, E₂′) through (E₆, E₆′) are notshown as well to keep clarity in the diagram.

[0031] Our Intent:

[0032] The intent of the above illustrations is to demonstrate that suchunique indentations can be made on a fastener in a particular pattern,which can be stamped on the fastener depending on the load and torquerequirements of the application. It should be obvious that there arenumerous other patterns possible, but the objective is to patent thegeneral concept of stamping a fastener with a series of indentationsalong the pitch line to suit the torque and preload needs of the jointand resist loosening of the same. Furthermore, such patterns being smallwould not appreciably degrade the strength and fatigue life of thejoint.

Appendix

[0033] [1] Nason, T. E. et al, “Self-locking fastener and method ofmaking same”, U.S. Pat. No. 3,182,702 filed Sep. 13, 1962.

[0034] [2] Criswell, Richard, “self-locking machine screw, U.S. Pat. No.5,704,748, Jan. 6, 1968.

[0035] [3] Orlomoski, R. W. “Self-locking screws”, U.S. Pat. No.3,517,717, filed May 3, 1968.

[0036] [4] Long-Lok Fasteners Corporation handbook, December 2002.

[0037] [5] Matsunami, S. “Self-locking fastener, U.S. Pat. No.6,135,689, Oct. 24, 2000.

[0038] [6] Iwata, Y. “Loosening and dislodging preventing screw, U.S.Pat. No. 5,672,037, Sept. 30, 1997.

1. Our claim is that this concept of stamping indentations along thepitch line of a fastener to increase its self-locking capability isnovel and has not been proposed by anybody previously. With decades ofexperience in the industry, we believe that such fasteners havingvariable O.D./nominal sizes, pitches/threads per inch and types ofmaterial when indented in such a novel way will preserve the preload andenhance torque capability under high thermal and vibratory loads.Various such patterns are possible and only two were described above forillustration. The objective is to patent this concept, as we believethat such fasteners when engineered appropriately, will be of great usein various industries where self-locking is required to preventloosening of the joint under repeated operations. Besides, thesepatterns being small would not reduce the strength of the boltsignificantly and hence fatigue life will be comparable to that of thevirgin fastener (before indentation). In fine, there are 2 independentclaims coupled with the dependent claims as follows: 1) Stamp a uniqueset of indentation patterns (geometry, size, number and styles arevariables) on a threaded fastener to: a) Increase engagement andself-locking capability b) Increase torque capability c) Achieve anydesired range of load, torque, strength and life required by varying thegeometry, size, number and style of indentation d) Achieve betterperformance under high thermal and vibratory loads 2) The aforesaidindentation patterns can be stamped on any fastener. a) Irrespective ofO.D./nominal size of the fastener b) Irrespective of pitch/threads perinch of the fastener c) Irrespective of material type of the fastener Inconclusion, this new threaded torque fastener concept will cater to thelong awaiting demand for self-locking fasteners in aerospace,automobile, and other industries, as well as in a harsh/high/cryogenictemperature environment applications requiring high strength of thefastener coupled with variable torque values.